Ultrasonic welding is one of the most practical joining method for polymer composite materials and has been adapted in the aerospace and automotive industries. To effectively join polymer composite assemblies, it is critical to understand the dynamic response of the welding system so that sound heating generation and welding sequences in the ultrasonic welding of the assemblies can be properly obtained. This study presents a dynamic response model of a multi-spot configuration assembly using ultrasonic welding. Here, a dynamic model of joining a U-shaped carbon fiber reinforced thermoplastic composite part with a flat part is developed and analyzed through the ratio between the frequencies generated at different locations of the spot with respect to the edges of the assembly and the natural frequency. Finally, this ratio is correlated with the weld quality of the multiple spot configuration. Guidelines for designing multisport sequence are extracted. This study provides a method to design the welding sequence in ultrasonic welding of carbon fiber reinforced composites.